Kerr cell



35o-391 S. Wal un V1000? OQ 1187219d`b Aug- 23, 1932 w. GALLAHAN 1,872,925

KERK CELL Filed Feb. 17. 1928 l 88. OPTGS,

Patented ug. 23, 1932 UNITED STATES PATENT OFFICE WALTER GALLAHAN, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR 10 WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VAN IA KEER CELL Application filed February 17, 1928. Serial No. 255,163.

This invention relates to Kerr cells and particularly to cells adapted for use in the photographic recording of sound.

One of the substances exhibiting a very large Kerr effect is nitro-benzol. This substance reacts with nearly all materials ordinarily used for either cementing or packing. This circumstance has rendered it difficult to build a container for the nitro-benzol which would not develop leaks and which would also protect the nitro-benzol from contamination.

The polarized light upon which the nitrobenzol is to act must be admitted to the container through a window and must emerge container and either metallic or carbon electrodes, but diiiiculties arise from the circumstance that the nitro-benzol either reacts chemically with the metal or contains impurities which will cause an electrolytic action between the liquid and the electrodes.

Moreover, fastening the glass in the windows has presented difficulties because, if gaskets are used, the reaction between them and the nitro-benzol results in the separation .Y of particles from the gaskets which, floating about in the nitro-benzol, interfere with the distribution of the electrostatic field or with the distribution of the light. Disturbing either of these distributions causes changes which manifest themselves as extraneous noises, when the sound record is used for reproduction.

Similar difliculties arise if, instead of a gasket, a cement is used for securing the glass in the windows.

It is preferable that the distance between the electrodes be small, otherwise a high potential must be used to obtain a Kerr effect of the desired magnitude. The space between the electrodes is accordingly reduced to a narrow crevice. It is advantageous to position such crevice vertically because then any dirt present in the nitro-benzol will, by settling, be removed from the field, also, any bubbles which happen to be present will, by rising, emerge from the field. It is preferable too, to have the space betwen the electrodes centrally located with reference to the windows. Danger of interference with the illumination of this space by the edges of the windows is thereby avoided.

The Kerr cell is associated with an optical system, in order to produce a powerful illumination in the space between the electrodes. The intensity of this illumination will change materially if the Kerr cell is improperly located with respect to the optical system.

Provisions for securing the correct relation between the optical system and the interelectrode space have been proposed which involve adjustment of the electrodes. It is not convenient to adjust the electrodes with the Kerr cell in position and, if it be removed from its position, in order to make such adjustment, it has heretofore been a difficult and tedious task to again place the cell in the correct position relative to the optical system.

Any provision for adjusting the electrodes involves movement of an electrode support relative to the wall of the cell. In order that the nitro-benzol shall not leak past the movable support, packing is necessary, but all packings heretofore proposed have been subject to the same objections as the gasket or cement mentioned above.

If, through any accident, the nitro-benzol becomes contaminated or the electrodes become dirty or the inner surfaces of the windows become dirty, it is necessary to empty the cell and wash it out. If the cell is made like a bottle, with only one orifice, such washing requires that the cell, partly filled with the Washing Huid, be agitated. The danger of scratching the inner surface of the windows or the proximate surfaces of the electrodes and the danger of breaking or dislocating the electrodes is increased by said agitation. If, however, the cell be provided with two orifices, a iow of washing fluid may be established through the cell and the parts thereby thoroughly cleaned. No agitation or other violent movement of either the cell or the fluid is then necessary.

It is an object of my invention to provide a Kerr cell in which the disadvantages heretofore experienced shall be avoided.

It is a further object of my invention t0 provide a Kerr cell which may be removed from the optical apparatus with which it cooperates and readily returned to a positively fixed position in the optical system.

It is a further object of my invention to secure the glass in the windows of a Kerr cell without gaskets or cement but by joints which will not leak.

It is a further object of my invention to provide means for the adjustment of the dilsltance between the electrodes of a Kerr ce It is a further object of my invention to provide a packing for the movable-electrode support which shall be incapable of reacting with nitro-benzol.

It is a further object of my invention to provide a Kerr cell in which all the surfaces in contact with the optically active liquid shall be incapable of reacting with said liquid and shall be unaffected by the action of said liquid.

It is a further object of my invention to provide a Kerr cell in which the electrode supports are surrounded by glass or quartz sleeves which form ground joints with the contiguous metallic parts. j

It is a further object of my invention to provide a Kerr cell which may be readily cleaned without the necessity of any violent relative motion between the cell and the cleaning material.

It is a further object of my invention to provide means whereby the position of an electrode relative to the cell may be adjusted and to provide means whereby the position of the cell, relative to external apparatus, may be reproduced at will.

It is a further object of my invention to provide means whereby thermal expansion of the liquid in a Kerr cell may occur with out producing high pressure, whereby leal:- age and danger of bursting are avoided.

It is a further object of my invention to provide a Kerr cell in which all metallic parts that may come into contact with the optically active liquid are plated with a metal incapable of reacting with said liquid.

Other objects of my invention and details of the co/nstruction will be apparent from the following description and the accompanying drawing, in which:

Figure 1 is a central vertical section;

Fig. 2 is a section on the line II`II of Fig. 1;

Fig. 3 is an enlarged section through one edge of the window, and

Fig. 4 is an enlarged section of one portion of the wall of the container.

The Kerr cell is formed from a main body or block 1 having a cavity 2. Preferably, the cavity is a circular cylinder having a horizontal axis. The upper edge of the block is provided with a groove 3 and the lower edge is provided with a groove 4. These grooves are accurately machined and serve to definitely position the cell with respect to the cooperating apparatus with which it is associated.

The cavity 2 is provided with an orifice 5, communicating with a vertical stand-pipe 6. The upper end of the stand-pipe is closed in any desired manner. In the form illustrated, the closure is a threaded stopper 7.

Diagonally opposite the orifice 5, the cavity 2 is provided with a second orifice 8 which communicates with the right-hand end surface of the cell through a threaded tubular passage, normally occupied by a screw 9. The head of the screw seats against a shoulder near the mouth of the passage.

The container is provided with two windows 11 and 12 on opposite faces of the cell. Circular holes 13 are provided in the faces of the cell to conform to the windows. The wall of the hole 13 has, near its outer opening, a cylindrical portion 14, adapted to fit closely but not tightly against a cylindrical Surface upon a ring 15. A shoulder 16 upon the ring contacts with a similar shoulder in the wall of the hole 13. From this shoulder to the external surface of the block 1, the mouth of the ring is bevelled, as shown at 17, and the edge of the ring 15 is correspondingly bevelled. The two bevelled surfaces are accurately ground to form, when pressed together, a joint through which nitro-benzol cannot leak.

The necessary pressure between the ground surfaces is provided by a plurality of screws 18, by means of which the ring 15 is secured in place on the body of the container. The glass of the window is seated against an inner surface of the ring, preferably in the same plane as the shoulder 16. The shoulder is separated from said surface by a web 19 of relatively thin metal. The inner edge of the web is bent over upon the glass or quartz and pressed or spun into place as indicated at 20. The glass being accurately ground and the surface against which it is seated also being accurately machined, it is possible to force the lip 20 against the glass so closely that the joint thus formed will not permit any leakage of nitro-benzol.

Within the container 2, a pair of electrodes 21 and 22 are mounted. These electrodes may be of metal or of carbon. Each electrode has a plane face disposed toward the 88. OPTICS,

other electrode. Extending from the opposite face toward the plane face, is a screwthreaded cavity in each electrode. If carbon electrodes are used, the carbon must be suitable for machining to provide such threads. The threads need not have any great strength because, as explained below, no mechanical stress is exerted upon them.

Screwed into the orifice of the electrode 21 is an electrode support 23 which is provided with a flange 24 adapted to contact with the face of the electrode 2l remote from the electrode 22. The stem 23 of the support is surrounded by a glass or quartz tube 25. One end of the glass or quartz tube contacts with the flange 24, and the other end contacts with a plate 26 which is integral with the block 1.

A washer 27 of insulating material surrounds the supporting stem 23 and contacts with the plate 26. A second washer 28 of conducting material carries a tab 29 to which, by soldering or in any other convenient manner, electrical connection may be made. The washers are confined in place by a nut 30 through which the stem 23 extends. The stem is threaded to cooperate with the nut, and the end of the stem is provided with a slot 31 to receive a screw driver.

A similar stem 32, provided with a flange 33, is screwed into the orifice in the electrode 22 and extends through the wall of the block.

1 opposite the wall in which the stem 23 is mounted. The stem 32 is surrounded by a glass or quartz tube 34 which, at one end, forms a ground joint with the flange 33 and, at the other end, is received into a cavity in a dog 35. The dog 35 is provided with a hole through which the stem 32 extends. For convenience in assembling, this hole, as shown at 36, is enlarged toward the small end of the dog 35. A nut 37 threaded upon the stem 32 makes contact with the dog 35.

The opening in the wall through which the stem 32 extends is larger than the glass tube 34. At the inner end of said opening, it is restricted to nearly fit the glass or quartz tube, as shown at 38. A bevelled surface connects the small inner end of the opening with the central portion thereof, and the central portion is filled with a packing material 39. In order to compress the packing 39 against the adjacent surfaces of the glass or quartz and the metal at 38, the outer port1on of the opening in the wall is screw-threaded, and a screw-threaded thimble 40, surrounding the tube 34, is screwed into the opening.

The packing material 39 is preferably a twisted or loosely spun form of pure cotton fibre. rIhe twisted packing material is first treated to remove from the cotton all traces of any impurities which may by any chance, react with nitro-benzol. The cotton is then thoroughly washed and soaked for several days in nitro-benzol before being placed in the gland. Then, when thimble 40 is screwed into place, the result is a joint which permits the electrode support to move longitudinally but prevents leakage of nitro-benzol.

A standard 42 is mounted in the end of the block l, through which the stem 32 extends. A second standard 43, mounted upon the same end of the block, is provided with a groove 44 which receives the end of the dog 35. The standards 42 and 43 may be either of insulation or metal. If the standard 43 is of metal, the dog 35 is of insulation.

A plate 45 is mounted upon the ends of the standards remote from the block 1 and secured in place by any suitable fastening, such as nuts threaded upon the ends of the standards. The shoulders between the threaded portion of the standards and the block afford a definite positioning means for the plate 45.

A recess or notch 46, in one edge of the plate 45, receives the stem 32. The threaded sleeve 47 is screwed u on the stem 32 and is rotatably confined wit in the recess 46. The portion of the sleeve 47 which is within the recess 46 is of reduced diameter. On the end of the sleeve toward the block 1, a flange 48 is provided and, on the opposite end of the sleeve, a head 49 is provided, each of larger diameter than the portion within the recess 46. The sleeve is thus prevented from moving horizontally by the presence of the plate 45 in the groove of the sleeve. The head 47 may, if desired, carry graduations 50 with numerals to enable any Ynoted position of electrode 22 to be reproduced.

The stem 32 is screw threaded to, or nearly to, the end which extends beyond the sleeve 47. At or near the end of the stem 32, two nuts 51 are provided which clamp between them a conducting washer, integral with a tab 52, by means of which an electrical connection may be made to the electrode 22.

Either the plate 45 or the sleeve 47 should be made of insulation, but it is not necessary that both of these members be insulating. All metal surfaces which come into contact with the nitro-benzol are electroplated with gold, as shown at 55, Fig. 4, before they are put into place.

In the assembly of the device, an abrading material, such as emery, is placed on the ends of the glass tube 25, and the tube is then placed on the stem 23. Tube and stem are then placed in the opening in the end of the block 1 opposite the stand pipe 6, by reaching through the space later occupied by windows. The washers 27 and 28 are then put in place on the projecting end of the stem. The nut 30 is screwed on the stem, but not far.enough to force the ends of the glass tube tightly against the flange 24 and the inner surface of the plate 26.

The stem 23 is now rotated by a screw driver inserted in the slot 31, and a grinding action takes place between the flange 24 and the adjacent end of the tube and also between the inner surface of the plate 26 and the end of the tube adjacent thereto. At intervals during this grinding operation, the nut 30 is loosened suiiiciently to permit the abrading material to assume a new distribution on the surfaces being ground and then tightened enough to cause the grinding to continue.

When the grinding operation is finished, the stem 23 is removed, the ends of the tube and the metallic surfaces ground against them are cleaned, the stem returned and the nut 30 tightened to bring the ground surfaces into intimate Contact. The electrode 21 is then screwed upon the threaded end of the stern 23 until it abuts the flange 24. Inorder that the longer dimension of the plane face of the electrode shall be vertical, the nut 3() is loosened, if necessary', and the electrode positioned by turning the stem by a screw driver in the slot 31.

The tube 34 is similarly supplied with an abrasive and placed on the stem 32. The dog 35 is then placed against the end of the tube 34, the nut 37 is screwed upon the stem 32, and a grinding operation, similar to that already described in connection with the tube 25. is performed upon the tube 34 and the surfaces contacting its ends.

The standards 42 and 43 are screwed into place. The nut 37 and the dog 35 are now removed, and the stem 32 with the tube 34 is inserted through the opening 38 by reach ing through the space which is to be occupied by the windows.

The soaked packing 39 is placed 1n the opening, and the thimble 40 is slipped over the end of the tube 34, and screwed against the packing. The dog 35 is replaced and the small end thereof is placed in the slot 44. The enlargement 36 of the hole through which the stem 32 extends permits the vertical movement of the dog which is necessary when placing the end in the slot.

The nut 37 is next screwed up on the stem 32 until it brings the ends of the glass or quartz tube 34 into loose contact with the ground surfaces of the flange 33 and the recess in the dog 35. The electrode 22 is then screwed up on the end of the stem 32 and, by means of a screw driver in the slot in the end of the stem, is rotated until the electrode is vertical. The nut 37 is then tightened until the clamping action of the nut and the end of the tube 34 on the dog 35 prevents rotation of the electrode support relative to the dog 35, which is prevented from rotating by its engagementwith the standard 43.

The sleeve 47 is next placed in the recess 46 of the plate 45 and, with the plate positioned in the groove of the sleeve, the sleeve is screwed upon the stem 32 until the plate 45 abuts the shoulders upon the standards 42 and 43.

The glass windows 12 and 13 are each mounted in its respective ring, and the bevelled surfaces 17 ground together to make a tight fit. The screws 18 are then put in place to secure the rings and windows in place.

In the operation of the device, the distance between the electrodes 21 and 22 is adjusted by rotating the sleeve 47. If any bubble is present in that portion of the cavity between the windows, it is caused to enter the stand pipe 6 by tilting the device. The device is then engaged with the cooperating apparatus by causing ribs upon the said apparatus to enter the grooves 3 and 4.

Polarized light from the optical system passes through the crevice between the electrodes 21 and 22, and an electrostatic field is established between them by connections through the terminals 29 and The degree of rotation of the plane of polarization caused by the nitro-benzol in the space between the electrodes is dependent upon the electric field, and, therefore, upon the potential impressed between the terminals 29 and 52.

lVhen a difference of potential is impressed upon the terminals 29 and 52, an electrostatic field is produced between the electrodes 21 and 22 because the electrode supports are insulated from the block 1 by the glass tubes 25 and 34 and the other insulating parts. The ground surface between the glass or quartz tubes and the flanges act to prevent access of nitro-benzol to the stem 23 and 32 but, as a further precaution against electrolytic or chemical action, the stems are gold plated.

If some slight amount of nitro-benzol gets into the interior of the glass or quartz tubes, the groundjoints between the end of the tube 25 and the plate 26, in one case or between the end of the tube 34 and the dog 35, in the other case, prevents further leakage.

Although I have specifically described only a single embodiment of my invention, many modifications will occur to those skilled in the art. I, therefore, do not intend to be limited except as necessitated by the prior art or indicated in the accompanying claims.

I claim as my invention:

1. In a Kerr cell, a container, an electrode therein, a supporting means for said electrode, including a metallic stem, a flange on said stem, an abutment means surrounding said stem on the opposite side of the container-wall from said flange, a vitric tube surrounding said stem and contacting with said flange at one end and with said abutment means at the other end, each of the ends and of the surfaces contacting being ground to form a joint through which the contents of the container will not leak.

2. In a Kerr cell, a container, an electrode UM Vl d wsdl therein, a supporting means for said electrode, including a metallic stem, a flange on said stem, an abutment means surrounding said stem on the opposite side of the container-wall from said ange, a glass tube surrounding said stem and contacting with said ange at one end and with said abutment means at the other end, each of the ends and of the contacting surfaces being ground to form a joint through which the contents of the container will not leak, and screw-threaded means for pressing said ground surfaces together.

3. In a Kerr cell, a container, an electrode therein, a supporting means for said electrode, including a metallic stem, a flange on said stem, an abutment means surrounding said stem on the opposite side of the container-wall from said flange, a vitric tube surrounding said stem and contacting with said ange at one end and with said abutment means at the other end, each of the ends and of the contacting surfaces being ground to form joints through which the contents of the container will not leak, and screw-threaded means for pressing said ground surfaces together, said electrode being on theside of said flange opposite the Vitric tube, whereby said pressure can cause no strain in said electrode.

4. In a Kerr cell containing nitro-benzol and having a gland in one wall through which a movable member extends, the method of packing the gland which consists in soaking a brous packing material incapable of chemical reaction with nitro-benzol in nitro-benzol until it can absorb no more nitro-benzol, placing the soaked material in the gland and compressing it in place.

5. In a Kerr cell, an electrode, a support therefor including a stem and a victric tube surrounding the stem, a member stationary with respect to the cell and contacting with one end of said tube and means on said stem for rotating it relative to said member, whereby the contacting surfaces of tube and member may be ground against each other.

6. In a. Kerr cell, an electrode, a support therefor, including a stem and a vitric tube surrounding the stem, a member stationary with respect to the cell and contacting with one end of said tube and means on said stem for rotating it relative to said member, whereby the contacting surfaces of tube and member may be ground against each other, and threaded means coacting with said stem to force said ground surfaces into close contact.

7. In a Kerr cell, a container, a pair of spaced electrodes within said container, means for adjusting the spacing of said electrodes, including a supporting stem extending from one electrode through the wall of the container, screw-threaded means for adjusting the position of said stem, said means including a member rotatably mounted on said wall of the container, and a device for preventing rotation of said stem, both said rotatable means and said preventing device including insulation electrically separating said stem from said container.

8. In a Kerr cell, a container, a pair of spaced electrodes within said container, means ilor adjusting the spacing of said electrodes, including a supporting stem extending from one electrode through the wall of the container, a plurality of standards mounted on said wall, an insulating plate carried by said standards, a nut threaded upon said stem and operatively associated with said plate to be thereby constrained from axial movement, an insulating member connected to said stem to rotate therewith and means on one of said standards cooperating with said member to prevent rotation thereof.

In testimony whereof, I have hereunto subscribed my name this 14th day of February, 1928.

VALTER GALLAHAN. 

